Doctor blades are known in the field of printing apparatuses, in particular rotogravure printing presses in which a gravure printing roller applies ink or the like onto a film or web material to be printed, such as a packaging material.
In a rotogravure printing press, the doctor blade is arranged adjacent and substantially parallel to the rotation axis of the printing roller, which is typically engraved according to the graphics or patterns to be printed onto the material. A pan containing the ink or other substances to be applied to the material is usually provided beneath the printing roller, in such a position that the printing roller can be wet by the ink or the substance in the pan during its rotation.
The material to be printed is generally fed to the printing roller by a pressing roller, which is in close proximity of the printing roller so that the material can contact a generating line of the printing roller downstream of the ink pan and can be printed according to the patterns engraved on the printing roller.
The doctor blade is placed downstream of the ink pan and upstream of the pressing roller, with respect to the rotation direction of the printing roller, and is aimed at wiping off the excess ink from the engraved surface of the printing roller before it contacts the material to be printed, so that the ink remains only in the patterned recesses engraved on the surface of the printing roller.
During the above printing process, a common problem is usually encountered, which is that unused ink can accumulate beneath the doctor blade and some ink can splash on the material to be printed and on the inner walls of the chamber enclosing the printing roller. As a consequence, without a periodic cleaning of the printing group, quality of print cycles degrades in time. Therefore, cleaning of the doctor blade unit, which is in close proximity of the printing color ink is an extremely important requirement to maintain excellent print quality.
Another known problem is that not any kind of ink can be used with rotogravure printing presses. For instance, some inks may be too fast drying or have too low viscosity, which makes them unsuitable to gravure printing presses because of the large extension of the rotation arc between the ink pan beneath the printing roller and the pressing roller, the latter being above the printing roller.
On the other hand, within a same printing plant, a print cycle may need inks for high quality applications and another print cycle may need inks for lower quality applications or adapted for different materials to be printed. This would require two independent print presses, e.g. a rotogravure printing press using a non-chambered doctor blade and a flexographic printing press using a chambered doctor blade, and a lot of space would be accordingly needed. Moreover, providing two different printing presses at the same plant would be very expensive and would double operation and maintenance activities.